This invention relates in general to cooking heating apparatus and more particularly to a cooking heating apparatus having a function to automatically control the charring operation of an object to be heated by detecting changes in the reflection factor of the surface of the object as the heating proceeds.
In cooking with a cooking heating apparatus, such as an electric oven, a gas oven or an oven range, wherein an object to be heated is put in a heating chamber and is subject to char cooking, it is conventional practice that the grade of the char condition of the object is estimated by a user through eye judgement or determined by a timer setting based on experience. However, the heating time for a desired grade of charring differs dependent on the quantity, water content, composition, shape and the like factors of the object to be heated and constant monitoring is required for attaining a proper grade of char.
To obviate this drawback, an automatic control for proper charring of an object to be heated has been proposed wherein a source of light is provided for irradiating visible rays on the object to be heated within a heating chamber, the intensity of reflection of the irradiated rays at the surface of the object is detected by a photo-sensor, and a heat generating source is controlled when the intensity of reflection reaches a predetermined magnitude.
This expedient for detection is acceptable in principle but has great difficulties to be solved before being put into practice. Namely, the optical system may be so contaminated by foreign materials or contaminants created upon heating the object, i.e. by scattered materials, that the intensity of irradiation rays onto an object to be heated as well as the intensity of reflected rays to be sensed by the optical sensor are decreased with the result that precise detection and control are impaired. Thus, how to keep the optical system substantially transparent with respect to light is unsolved with the above expedient.